Residual charges and infrared absorption in electrochromic WO3 films prepared by hydrogen-introduced sputtering

Electrochromic WO3 films were prepared by rf-sputtering in atmosphere consi sting of Ar/H-2/O-2 mixed gas. The as-sputtered films require several times of injection/extraction of ions (the aging) for obtaining reversible color ation/bleaching. After the aging, there are ions (protons) remaining in the films, namely residual charges. From the results of IR absorption of the a s-sputtered and aged films, the residual charges contribute to create OH an d HOH bonds. Hydrogen introduced in the films during sputtering is transfor med only into OH bonds combining with unstable oxygen in the films. The int roduced hydrogen is considered to suppress the growth of grain in WO3 films from AFM observation. (C) 2001 Elsevier Science BN. All rights reserved.